The invention relates to a pedicle screw having a threaded shaft part and a receiver part provided at the head side of the threaded shaft part and being adapted for receiving a bar.
Such screws are used in the monosegmental or multisegmental fixation of the spinal column. A predicle screw of this kind is known from the German patent specification No. 26 49 042. The screw comprises a threaded portion and a receiver portion rigidly connected thereto at the head end. Several pairs of such screws are screwed into the vertebrae on both sides of the spinal column in a respective distance from each other. The respective receiver portions comprise receiving slits. A respective threaded bar is passed thorugh these receiving slits of the right and left group of the screws. Thereafter the bar is fixed to the respective receiver portion by means of fastening screws. It is a drawback of this solution that it is difficult to rigidly screw these screws into the vertebrae and at the same time position the screws in two planes in exactly such a manner that the axes of the receiving slits in the receiver parts in the vertical columns are aligned such that the threaded rod may be passed through the receiving slits without distortion of the screws. Even the attempt to do this requires a lot of time which is very disadvantageous for an operation at the spinal column. Moreover such an exact alignment can hardly be achieved. As a result relevant shearing forces act upon the threaded rods which causes a possible break of the rods in use after the operation or a lack of fixation.